Tesco has been warned over its pricing policies by the advertising watchdog following a complaint about a sales promotion for beer.
The supermarket giant advertised four cans of Hobgoblin on its website for £4.50 on October 23, claiming this was a 49p saving on the original price of £4.99.
A bright yellow shelf sticker said the deal was available until November 12.
But one customer complained that the beer had been available for £4 for three months until October 7, and was still being sold at the lower £4.50 price after the promotion ended.
Tesco said the beer had been priced at £4.99 from October 2 until October 22, a total of 21 days.
They said the price was consistent with other retailers in the market and believed that customers accepted £4.99 as a genuine price for the product.
They said they had agreed to adhere to the Office of Fair Trading's guidelines on food pricing and promotions at the end of 2012, meaning that they would not advertise a product as being on promotion for a period longer than that product had been available at a higher price.
Tesco agreed that it continued to sell the product at £4.50 from November 13 to December 3 "to reflect other retailers' selling price", but this was not communicated to customers as a promotion and the price was featured on a regular white shelf label during that time.
The Advertising Standards Authority (ASA) said consumers were likely to understand that £4.99 was the usual selling price for the product and Tesco had reduced the price for the promotional period, meaning they benefited from a saving of 49p.
The ASA said: "Although we acknowledged that the product category was one in which prices fluctuated regularly, we considered that, because the product had been available at £4 for at least two of the three months leading up to the promotion, and for at least twice as long as it had been available at the higher price referenced in the ad, it was reasonable to assume that £4 was the normal selling price for the product at the time the ad was seen.
"Because of that, and because we considered that the ad implied that £4.99 was the normal selling price for the product, we concluded that the promotion was likely to mislead consumers into believing that a greater saving was available than was the case."
It also found that the inclusion of a closing date in the ad implied that the price would be increased to £4.99 after that date, but "because that was not the case, we concluded that the ad was likely to mislead in that respect".
It ruled that the ad must not appear again in its current form, adding: "We told Tesco Stores Ltd to ensure that prices used as the basis of savings claims reflected the normal selling price for the product and not to imply that a product would revert to a higher price if that was not the case."
A Tesco spokesman said: "We aim to offer prices and promotions that help our customers manage the cost of their shopping.
"We constantly review our pricing and Trading Standards has acknowledged that we are amongst the most vigilant in the industry for complying with their guidelines."
Which? executive director Richard Lloyd said: "Special offers should be special. We've found dodgy deals across the aisles, with prices yo-yoing between multi-buys and discounts so that it is almost impossible to know the actual price.
"We're campaigning for simpler, clearer and fairer pricing rules and tougher enforcement action."